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Measurement method of electric clearance and creepage distance in PCB design
With the rapid development of science and technology and the continuous improvement of people’s living standards, more and more electronic products enter our homes. In order to ensure the personal safety of users, all countries in the world have relevant laws and regulations to restrict the personal damage caused by electrical products. All kinds of injuries. Therefore, the safety design plays a vital role in the entire design process of the product, and the safety distance is one of the most important parts in the product design. There are often different results in the actual measurement of electrical clearance and creepage distance. This article combines its own actual work to make a general summary of the safety standard requirements for electrical clearance and creepage distance, and talk about the following points of understanding.

one. Glossary:

1. The safety distance includes electrical clearance (spatial distance), creepage distance (creepage distance) and insulation penetration distance.

2. Electric clearance: the shortest distance measured along the air between two adjacent conductors or a conductor and the surface of the adjacent motor casing.

3. Creepage distance: the shortest distance between two adjacent conductors or one conductor and the surface of the adjacent motor casing measured along the insulating surface

Leave.

4. Primary circuit: The primary circuit is a circuit directly connected to the AC power grid.

5. Secondary circuit: The secondary circuit is not directly connected to the primary

A device or equivalent isolating device or a circuit powered by a battery.

two. Understanding from the definition of clause 2.10 in GB4943-2001:

In GB4943; Clause 2.10, it is pointed out that the size of the electrical gap should be such that the transient overvoltage entering the equipment and the inside of the equipment

The peak voltage generated cannot make it break down. The size of the creepage distance should be such that the insulation is at a given working voltage and pollution level

There will be no flashover or breakdown (tracking). It can be seen that the prevention objects and assessment objectives of electrical clearance and creepage distance

s difference. The electric gap prevents transient overvoltage or peak voltage; while the creepage distance is to assess the insulation in a given working voltage.

The ability to withstand pressure and pollution levels.

From the definition of the terms of the primary circuit and the secondary circuit, it can be seen that the secondary circuit may be safe and accessible, or it may be

Dangerously charged; there may be both a primary circuit and a secondary circuit in a device, for example, it is scheduled to be directly connected to the power grid

The power adapter used; a device may itself be a secondary circuit, such as a generator or battery powered

equipment. On the basis of understanding and distinguishing between primary and secondary circuits, we also understand why there are also secondary circuits in the standard

Requirements for electrical clearance of basic insulation, additional insulation, reinforced insulation, etc.

The specific measurement steps are as follows:

1) Measurement steps of electrical clearance:

Determine the peak value and effective value of the working voltage;

Determine the power supply voltage and power supply facility category of the equipment;

Determine the magnitude of transient overvoltage entering the equipment according to the overvoltage category;

Determine the pollution level of the equipment (generally equipment is pollution level 2);

Determine the insulation type (functional insulation, basic insulation, supplementary insulation, reinforced insulation) that the clearance spans.

2) Steps to determine the creepage distance

Determine the effective value or DC value of the working voltage;

Determine the material group (according to the comparative tracking index, it is divided into: group 1. material, group 2 material, group 3a material, 3b

Group of materials. Note: If the material group is not known, the material is assumed to be group IIIb)

Determine the pollution level;

Determine the insulation type (functional insulation, basic insulation, additional insulation, reinforced insulation)

The required value of electric clearance and creepage distance:

The electrical clearance is based on the measured working voltage and insulation level, check the table (GB4943: 2H and 2J and 2K, 60065-2001

Table: Table 8 and Table 9 and Table 10) The distance can be determined by searching the required clearance; as an alternative method of clearance,

4943 uses appendix G to replace, 60065-2001 uses appendix J to replace.

The creepage distance is based on the working voltage, insulation grade and material group, check the table (GB4943 is table 2L, 65-2001 is table

11) Determine the creepage distance value. If the working voltage value is between the two voltage ranges in the table, you need to use the inner difference method to calculate it.

Creepage distance.

*In GB 4943, only the electrical clearance and creepage distance of functional insulation can be reduced, but it must meet the standard 5.3.4

Set high voltage or short circuit test.

three. Understanding from the definition of clause 13 in GB8898-2001:

The main factor considered for electrical clearance in clause 13 of GB8898-001 is working voltage, which can be determined by referring to Figure 9. (right

Components that are electrically connected to the grid power supply with the effective value of the voltage in the range of 220-250V, these values are equal to 354V peak

Those values corresponding to the voltage: basic insulation 3.0mm, reinforced insulation 6.0mm).

GB 8898-2001 The judgment value is equal to the electrical clearance, if the following three conditions are met, the electrical clearance and creepage distance

Reinforced insulation can be reduced by 2mm, and basic insulation can be reduced by 1mm.

1. These creepage distances and electrical clearances will be reduced by external forces, but they are not in the accessible conductive parts and dangers of the shell

Between live parts;

2. They remain unchanged by the rigid structure;

3. Their insulation characteristics will not be seriously affected by the dust generated inside the equipment.

*Note: However, the insulation, creepage distance and electrical clearance between components of different polarities directly connected to the grid power supply are not

Allow to reduce. Even if basic insulation and supplementary insulation do not meet the requirements of creepage distance and electrical clearance, as long as the insulation is short-circuited,

If the equipment still meets the standard requirements, it is acceptable (Article 4.3.1 of 8898).

The above is an introduction to the measurement methods of electrical clearance and creepage distance. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology